The Chromium Visual Debugger App is the viewer for the debug stream from a (remote) chromium instance. For information on the chromium integration of debug capture see: //components/viz/service/debugger/README.md
To use the Visual Debugger, Chromium must be launch with remote debugging support.
$ ./chrome --remote-debugging-port=7777 --remote-allow-origins=*
To launch the Debugging App simply run the python server from this directory. The default port is 7777.
$ tools/visual_debugger/server.py [portnumber]
This command will also launch the debugger as a Web App in a separate instance of the default browser.
In official builds (is_official_build=true gn arg) the debugger is disabled by default but can be force enabled locally with the flag below in args.gn.
use_viz_debugger=true
In order to connect to an Android device it must be launched with the args above and connected via USB to your development machine. Android ADB can then be setup to forward Chrome Devtools Protocol to the remote port, for example if you used --remote-debugging-port=7777 when launching Chrome you would run the following.
$ adb forward tcp:7777 localabstract:chrome_devtools_remote
Once the Debugging App launches one should be able to simply click Connect to establish a remote debugging stream to the live instance of chromium.
The in App filters frame.root.quad and frame.root.damage have been provided by default to give immediate feedback and intuition. The debug macros corresponding to these filters, and all others, can be found directly in the source.
The debugging macros feed information into the VizDebugger static instance. At the end of each frame this cached information is fed upstream and eventually reaches the remote client.
The Debugger App preforms nominally in most basic debugging situations. Excessive debug logging, specifically text, can make the App feel sluggish. It is recommended to delete unused filters and disable filters to improve App performance.
For official builds all visual debug macros end up as chrome traces. This means there are minimal security concerns for this system with exception of mutable side effects in the creation of input variables to the logging macros. These concerns for mutable side effects already exist for any other code; so no special attention is warranted for these macros.
For non-official (debug) builds the dev-tools remote debugging port command line argument must be provided for the viz debugger to collect and stream data. Thus the security of this new system is identical to that of the remote dev tools for the case of debugging builds.
For official builds the visual debugger is disabled but the logging feeds into the chrome tracing system. This visual debugger specific tracing is reported with the ‘viz.visual_debugger’ tracing category. These traces can be imported into the visual debugger using the import trace button.
The overhead of these optional traces has been evaluated and the cost has been found to be acceptable. Trace Macro Overhead in Official Builds
